Low temperature reduction of metal oxides

Abstract

Disclosed herein is a method for reducing a metal oxide in a metal oxide containing precursor. The method comprises providing a reaction mixture comprising the metal oxide containing precursor and an aluminium reductant; heating the reaction mixture in the presence of solid or gaseous aluminium chloride to a temperature at which reactions that result in the metal oxide being reduced are initiated; controlling reaction conditions whereby the reaction mixture is prevented from reaching a temperature at which thermal runaway can occur; and isolating reaction products that include reduced metal oxide.

The invention claimed is: 
     
       1. A method for producing a powder comprising silicon, the method comprising:
 providing a reaction mixture comprising a silicon oxide containing precursor and an aluminum reductant; 
 heating the reaction mixture at atmospheric pressure in the presence of gaseous aluminum chloride or a mixture of solid and gaseous aluminum chloride to a temperature of between 300° C. and 600° C., whereby reactions that result in the silicon oxide being reduced are initiated, the amount of the aluminum chloride being between 1 wt % and 500 wt % of the weight of the silicon oxide containing precursor; 
 controlling reaction conditions to maintain the temperature below 650° C., whereby the reaction mixture is prevented from reaching a temperature at which thermal runaway can occur and whereby the formation of aluminium oxychloride as a by-product is favored over aluminum oxide; and 
 washing products of the reaction in dilute acid to isolate the silicon powder. 
 
     
     
       2. A method for producing a powder comprising silicon, the method comprising:
 feeding a silicon oxide containing precursor and an aluminum reductant into a reaction vessel at atmospheric pressure and at a temperature of between 300° C. and 600° C., in the presence of gaseous aluminum chloride or a mixture of solid and gaseous aluminum chloride; 
 mixing the reactants together and in the presence of reaction products that form; 
 controlling a feed rate of the silicon oxide containing precursor and the aluminum reductant into the reaction vessel such that the temperature in the reaction vessel does not exceed 650° C.; and 
 washing the reaction products in dilute acid to remove aluminum oxychloride by-product and isolate the silicon powder. 
 
     
     
       3. The method of  claim 1 or claim 2 , where the solid aluminum chloride is provided in the form of a powder or granules of aluminum chloride with a particle size less than 5 mm. 
     
     
       4. The method of  claim 1 , wherein the silicon oxide containing precursor, aluminum reductant, and solid aluminum chloride in the reaction mixture are independently provided in the form of a powder, flakes, fibers or particulates. 
     
     
       5. The method of  claim 1 or claim 2 , wherein the aluminum reductant is aluminum or an aluminum alloy in the form of a powder or flakes with a particle size of less than about 50 μm in at least one dimension. 
     
     
       6. The method of  claim 1 or claim 2 , wherein the amount of the aluminum reductant is between 5 wt % and 500 wt % of the weight of the silicon oxide containing precursor. 
     
     
       7. The method of  claim 1 or claim 2 , wherein the reaction mixture is heated in an inert atmosphere. 
     
     
       8. The method of  claim 1 , wherein the reaction conditions are controlled by one or more of gradually feeding additional one or both of the silicon oxide containing precursor and the aluminum reductant into the heated reaction mixture; by cooling the reaction mixture by external means; and/or using a thermal load moderator to the reaction mixture. 
     
     
       9. The method of  claim 1 or claim 2 , wherein gaseous aluminum chloride formed during the reaction is condensed for recycling back into the reaction mixture. 
     
     
       10. The method of  claim 1 or claim 2 , wherein the silicon powder is a powder of silicon or a mixture of silicon and SiO 2  having a particle size of less than 500 nm. 
     
     
       11. The method of  claim 1 or claim 2 , wherein the reduction reaction is carried out at a temperature of between 450° C. and 600° C. 
     
     
       12. The method of  claim 1 or claim 2 , wherein the reduction reaction is carried out at a temperature of between 400° C. and 550° C. 
     
     
       13. The method of  claim 1 or claim 2 , wherein alloying additives are included with the silicon oxide containing precursor, the alloying additives include one ore more of pure elements, chlorides, oxides or nitrides based on Zn, Cu, Fe, Ni, Co, Cr, Mo, Sn, Ti, In, Sb, Ag, V, Mn, Pt, Pd, Ta, Zr, Nb, Rh, Ru, Os, Re, C, B and W.